In the quiet night of 1986, the Lake Nyos disaster in Cameroon mysteriously claimed the lives of over 1,700 people, leaving many questions unanswered. After years of research, scientists have uncovered the causes and preventive measures, but are we ready to prevent a similar disaster from happening again? Explore the mystery and the relentless efforts to better understand one of the world’s most bizarre and dangerous natural phenomena.
The terrible disaster begins
Mysterious Deaths
On the morning of August 22, 1986, a man riding his bicycle from the village of Wum in Cameroon to the village of Nyos saw a dead antelope lying by the roadside. After tying the antelope to his bicycle, the man continued on and discovered the bodies of two rats, a dog, and two other animals.
He arrived at a tent area ahead to inquire, wondering if they had been struck by lightning. Upon entering the tent, the man was horrified to find dead people lying everywhere. He searched around but found no survivors and hurriedly rode back to Wum.
Upon returning to Wum, he encountered survivors from Nyos and neighboring villages. They recounted hearing a loud explosion, followed by a foul smell that caused them to pass out. When they regained consciousness, everyone around them was dead.
After receiving reports from local authorities, the Cameroon government sent a team to investigate. Due to Wum’s remote location, the medical team took two days to reach the scene.
The doctors were astonished to learn that the number of fatalities reached 1,746, much higher than they had imagined. This did not include victims buried by survivors in a large mass grave.
Additionally, more than 3,000 livestock along with numerous wild animals, birds, and insects also mysteriously died overnight.
The autopsy results provided very little information. There were no signs of bleeding, injury, or illness, nor were there indications that the victims suffered before dying. They simply collapsed, lost consciousness, and died. Additionally, there were no signs of exposure to radiation, chemical weapons, or toxic gases.
Legends and the people’s terror
Due to extreme fear and trauma, many survivors fled the village and hid in the forests. What could have taken so many lives in such a short period of time? Numerous researchers from around the world, including France and the USA, came to Cameroon to find the answer.
One of the first important clues was Lake Nyos, also known as the ‘evil lake.’ Ancient legends tell of a time long ago when evil spirits escaping from the lake killed all the villagers living near its shores.
The cause of the mysterious deaths
The initial investigation process
The bodies of the victims were primarily concentrated within a 20 km radius around the lake. The closer to the lake, the higher the number of dead bodies. Villages farther from the lake had more survivors, especially those who stayed indoors. In Nyos, the village closest to the lake, less than 4 km away, only 6 out of over 800 villagers survived.
Lake Nyos is originally a lake formed on an extinct volcanic crater, approximately 2.5 km² in size with the deepest point at 210 m. After the disaster, the clear blue water of the lake suddenly turned red and murky. Based on this clue, scientists believed that the volcano beneath the lake had reactivated. A possible eruption of toxic gas could be the culprit behind these mysterious deaths.
This hypothesis sounds convincing but has a weakness. An eruption capable of releasing enough toxic gas to kill so many people over such a wide area would likely be accompanied by seismic activity. However, survivors reported that there was no earthquake at the time of the disaster.
Furthermore, data from a seismic station more than 200 km away from the site also showed no unusual activity on the night of August 21. The belongings and stacks of goods inside the homes of the victims remained intact, undisturbed.
The real cause of the disaster
Subsequently, scientists discovered an extremely important clue: the oil lamps in the homes were all extinguished, even those that still had plenty of oil.
They began testing water samples taken from different depths of Lake Nyos. The red color on the surface of the lake turned out to be iron, which is usually found at the bottom of the lake. For some reason, the sediment at the bottom had been disturbed, causing the iron in the lake to rise to the surface, react with oxygen, and turn red.
The CO2 concentration in the lake water was abnormally high. A water sample taken from a depth of 15 meters contained so much CO2 that when brought to the surface, the CO2 created bubbles as if someone had just opened a can of soda. The deeper the water, the higher the concentration of CO2. At a depth of 182 meters, the water sampling equipment exploded due to the immense pressure of the gas. Scientists had to use a special pressure-adjusted container to collect the water samples. They were quite surprised to find that the amount of dissolved CO2 was five times greater than the amount of water.
Piecing together these clues, scientists developed a hypothesis about the accumulation of CO2 gas. The volcano under Lake Nyos had been inactive for a long time, but the magma was still active underground and releasing carbon dioxide not only into the lake but also into the surrounding environment. Since CO2 is heavier than air, it would concentrate near the ground before being dispersed by the wind. In fact, Cameroon frequently experienced incidents where frogs and small ground-dwelling creatures died from CO2 asphyxiation.
Not only Lake Nyos, but all lakes contain CO2 gas. Typically, the gas bubbles to the surface and dissipates into the air, rather than accumulating at the bottom. Rain, cold air, and wind cause the surface water to cool, become denser, and sink. This colder water displaces the warmer, CO2-rich water, pushing the CO2 out where it disperses into the air.
Later, scientists discovered that Lake Nyos is one of the calmest lakes in the world. High hills surrounding the lake block the wind, creating uniform water temperatures from the surface to the bottom. Because Nyos has a tropical climate with constant warm temperatures year-round, the water temperature does not vary much from season to season. Moreover, because the lake is so deep, even if the surface water temperature changes, the cold water cannot sink to the bottom. The stillness of Lake Nyos’ water is precisely what makes it so dangerous.
Because the bottom of Lake Nyos was saturated, CO2 was pushed up to the low-pressure water layers. At this point, a small external disturbance such as a gust of wind or a landslide was enough to cause the gas to rapidly escape into the air. During this process, a chimney effect might occur, triggering a chain reaction, causing Lake Nyos to release all the accumulated CO2 at the bottom over decades.
CO2 gas is odorless, colorless, and non-toxic. Normally, air contains 0.05% CO2. However, if the concentration reaches 10%, CO2 can be lethal. A concentration of 5% can extinguish fires. This explains why all the oil lamps in the victims’ homes were extinguished.
Months after the Lake Nyos disaster, scientists continued to monitor the gas levels in the lake. When they saw the CO2 levels rising again, they confirmed that their previous hypothesis was correct. Moreover, they estimated the amount of CO2 that had escaped from the lake on August 22.
Previously, on August 17, many reported seeing Lake Nyos bubbling strangely, creating clouds of white smoke above the surface of the lake. Five days later, Lake Nyos suddenly exploded, creating huge water columns tens of meters high. Scientists estimated that Lake Nyos had released 1.2 km³ of CO2 gas, enough to fill 10 soccer stadiums in 20 seconds.
The CO2 rose high before settling back down to the surface of the lake. Livestock grazing on high hills hundreds of meters above were killed. After that, the layer of gas swept down into the valley at a speed of 72 km/h. Those living by the lake had no chance to escape. Very few on the slopes were alert enough to climb to higher ground and survive. One surviving witness said he jumped on his motorcycle and sped to safety as soon as he saw his neighbor collapse in the gas cloud. Most victims did not realize the danger until the gas enveloped them.
In villages far from the lake, the chances of survival were higher. However, many curious about the loud sound of the gas explosion ran outside to investigate, inhaled the toxic gas, and died right in front of their homes. The death of a victim would prompt others in the house to run outside and meet a similar fate. Some described the thunderous sound of the explosion as resembling gunfire.
On the other hand, those who stayed inside with windows and doors closed survived. There were also instances where CO2 seeped through cracks in doors and entered homes, but only killed those who were lying down; those standing did not die because their heads were above the level of the toxic gas. A few survivors were unaware of what had happened until they discovered that all their sleeping family members had died.
Similar disasters
The Lake Nyos disaster is the second CO2 gas eruption disaster in history. Two years earlier, on August 15, 1984, a major explosion from Lake Monoun, located on a volcanic crater not far from Lake Nyos, killed 37 people. Of these, 17 died while passing through a depression where a large concentration of CO2 had accumulated. Because there were relatively few casualties, the incident did not receive much attention.
Preventing a disaster from recurring
Relocating residents
Today, scientists believe that only three lakes in the world—Nyos, Monoun, and Kivu, located between the borders of Congo and Rwanda—accumulate enough dissolved CO2 at the bottom to be lethal. When Lake Nyos began to accumulate CO2 again, the government of Cameroon forced the residents of the villages around the lake to relocate. They dismantled the houses to prevent anyone from returning before the area around the lake was deemed safe again.
Using CO2 venting pipes
It took about a year to determine the cause, and then scientists spent another ten years finding ways to release the CO2 and prevent the disaster from recurring. They installed a pipe with a diameter of 13 cm down to a depth of 182 meters, just above the lakebed. Water from the bottom layer was pumped through the pipe, spraying upwards to release the CO2 gas. This process continued until all the CO2 at the bottom of the lake was released. After successful testing in 1995, the venting pipe was officially put into use in 2001.
By the autumn of 2006, the venting pipe was still functioning well and releasing nearly 20 million cubic meters of gas each year, which was more than the amount of gas being absorbed into the lake. From 2001 to 2006, the amount of CO2 in Lake Nyos decreased by 13%.
Reinforcing the dam
Nevertheless, scientists are concerned that this reduction is still too low, while the CO2 levels in Lake Nyos have doubled compared to 1986. An even greater concern is the natural dam to the north of Lake Nyos, which is eroding and at risk of collapsing within less than five years. If the dam breaks, a horrific disaster will occur. 50 million cubic meters of water will flow into the lake, creating a flood that will sweep through the valley and submerge tens of thousands of people. After the flood, the water level in the lake will significantly decrease, removing the water pressure that acts like a ‘plug’ to contain the CO2 gas at the bottom of the lake. The amount of CO2 released will be much greater than in 1986.
To address this issue, scientists have proposed a project to reinforce the natural dam with concrete and to install four additional venting pipes to maintain the CO2 concentration at a safe level for the next four years. They are actively fundraising to implement the project as soon as possible. Professor George Kling from the University of Michigan, who has studied Lake Nyos for over 20 years, stated: ‘A disaster could occur at any time and be much more catastrophic than before. Each day that passes, the risk of disaster increases.
The Lake Nyos disaster underscores the critical need for vigilant scientific monitoring and proactive disaster management. Efforts to stabilize Lake Nyos and prevent future tragedies highlight the ongoing challenge of natural hazards. This event serves as a stark reminder of the importance of preparedness and global awareness in handling geological phenomena.
